Capital and Financing Transactions - Mortgage Notes Payable (Details) (USD $)	0 Months Ended	12 Months Ended				0 Months Ended						0 Months Ended	12 Months Ended		12 Months Ended			0 Months Ended	12 Months Ended			12 Months Ended				12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended									0 Months Ended		0 Months Ended		6 Months Ended			0 Months Ended
	Mar. 09, 2012 sqft	Dec. 31, 2013 sqft	Dec. 31, 2012	Sep. 28, 2012	Feb. 10, 2012	Feb. 10, 2012 Minimum [Member]	Feb. 10, 2012 Maximum [Member]	Jan. 09, 2012 111 East Wacker, LLC [Member]	Feb. 10, 2012 Hayden Ferry II [Member] sqft	Feb. 10, 2012 Hayden Ferry II [Member] Minimum [Member]	Feb. 10, 2012 Hayden Ferry II [Member] Maximum [Member]	Nov. 15, 2012 Westshore Corporate Center [Member]	Dec. 31, 2013 Westshore Corporate Center [Member]	Dec. 31, 2012 Westshore Corporate Center [Member]	Dec. 31, 2013 NASCAR Plaza [Member]	Dec. 31, 2012 NASCAR Plaza [Member]	Dec. 31, 2012 Fund I Remaining Assets [Member]	Jan. 09, 2012 The Pointe [Member]	Dec. 31, 2013 The Pointe [Member]	Dec. 31, 2012 The Pointe [Member]	Jan. 11, 2012 The Pointe [Member]	Dec. 31, 2013 Corporate Center Four at International Plaza [Member]		Dec. 31, 2012 Corporate Center Four at International Plaza [Member]		Dec. 31, 2013 Phoenix Tower [Member]	Feb. 21, 2013 Phoenix Tower [Member] sqft	Dec. 31, 2012 Phoenix Tower [Member]	Dec. 31, 2013 Lincoln Place	Dec. 31, 2012 Lincoln Place	Dec. 31, 2013 CityWestPlace I and II [Member]	Dec. 31, 2012 CityWestPlace I and II [Member]	Dec. 31, 2013 CityWestPlace III and IV [Member]	Dec. 31, 2012 CityWestPlace III and IV [Member]	Dec. 31, 2013 San Felipe Plaza [Member]	Dec. 31, 2012 San Felipe Plaza [Member]	Dec. 31, 2013 Hayden Ferry Lakeside II [Member] sqft	Jun. 28, 2013 Hayden Ferry Lakeside II [Member] sqft	Feb. 10, 2012 Hayden Ferry Lakeside II [Member]	Mar. 09, 2012 Bank of America Plaza [Member]	May 31, 2012 The Pinnacle at Jackson Place [Member]	Dec. 31, 2013 Pinnacle at Jackson Place - Sr NMTC Loan [Member]	Dec. 31, 2012 Pinnacle at Jackson Place - Sr NMTC Loan [Member]	May 31, 2013 Mortgages [Member] Corporate Center Four at International Plaza [Member] sqft	Aug. 01, 2013 Mortgages [Member] Corporate Center Four at International Plaza [Member]	Feb. 21, 2013 Mortgages [Member] Phoenix Tower [Member]	Mar. 07, 2013 Mortgages [Member] Deerwood Portfolio [Member]	Jun. 27, 2013 Hayden Ferry II Original Mortgage [Member] Hayden Ferry Lakeside II [Member]	Jun. 28, 2013 Hayden Ferry II Original Mortgage [Member] Hayden Ferry Lakeside II [Member]	Aug. 01, 2013 Hayden Ferry II Modified Mortgage [Member] Hayden Ferry Lakeside II [Member]	Feb. 10, 2012 London Interbank Offered Rate (LIBOR) [Member] Hayden Ferry II [Member]	Feb. 10, 2012 London Interbank Offered Rate (LIBOR) [Member] Hayden Ferry II [Member] Minimum [Member]	Feb. 10, 2012 London Interbank Offered Rate (LIBOR) [Member] Hayden Ferry II [Member] Maximum [Member]	Jun. 28, 2013 London Interbank Offered Rate (LIBOR) [Member] Hayden Ferry II Modified Mortgage [Member] Hayden Ferry Lakeside II [Member]	Jun. 28, 2013 London Interbank Offered Rate (LIBOR) [Member] Hayden Ferry II Modified Mortgage [Member] Hayden Ferry Lakeside II [Member] Minimum [Member]	Jun. 28, 2013 London Interbank Offered Rate (LIBOR) [Member] Hayden Ferry II Modified Mortgage [Member] Hayden Ferry Lakeside II [Member] Maximum [Member]	Dec. 31, 2013 Office Building [Member] CityWestPlace I and II [Member] Mortgages [Member]	Dec. 31, 2013 Office Building [Member] San Felipe Plaza [Member] Mortgages [Member]	Dec. 31, 2013 Office Building [Member] CityWestPlace III and IV [Member] Mortgages [Member]	Dec. 19, 2013 Office Building [Member] CityWestPlace [Member] Mortgages [Member]	Dec. 06, 2013 FLORIDA Office Building [Member] Lincoln Place sqft	Dec. 31, 2013 FLORIDA Office Building [Member] Lincoln Place Mortgages [Member]	Dec. 06, 2013 FLORIDA Office Building [Member] Lincoln Place Mortgages [Member]	Dec. 31, 2013 Debt Balloon Payments [Member]	Dec. 31, 2013 Debt Principal Amortization [Member]
Debt Instrument [Line Items]
Collateral for Mortgage Loans		$ 1,700,000,000	$ 947,200,000
Basis spread on variable rate (in percent)						2.50%	3.50%																																													2.50%	3.50%		2.50%	3.50%
Fixed rate (in percent)	7.10%											2.50%	2.50%		3.40%	3.40%			4.00%		4.00%	4.60%	[1]			3.90%			3.60%		6.20%		5.00%		4.80%							5.80%															6.20%	4.80%	5.00%			5.90%
Mortgage loan maturity date												May 01, 2015	May 01, 2015		Mar. 30, 2016	Mar. 30, 2016		Feb. 10, 2019	Feb. 10, 2019			Apr. 08, 2019	[1]			Mar. 01, 2023			Jun. 11, 2016		Jul. 06, 2016		Mar. 05, 2020		Dec. 01, 2018
Gross sales price of property								150,600,000
Mortgage loans assumed by buyer for property sold								147,900,000									76,700,000																								29,500,000
Mortgage assumed by buyer for property acquired												14,500,000				42,600,000
Proportionate share of mortgage loan									15,000,000								19,200,000
Mortgage notes payable									50,000,000.0																														50,000,000					36,000,000
Area of real estate property (in square feet)	337,000	17,600,000							300,000																		629,000										300,000	299,000						250,000																	140,000
Weighted average interest rate on loans (in percent)										4.00%	5.00%																														5.20%				4.60%
Mortgage loan maturity date	May 2012							July 2016	July 2018
Interest rate on mortgage (in percent)					1.50%			6.30%				5.80%				4.70%																														3.90%	3.90%																5.90%
Amortization period of principal amount of loan (in years)																																														25 years	30 years
Interest only period of mortgage																		0 years 43 months 0 days																										24 months			3 years
Notional amount				125,000,000																																							23,501,000	13,500,000.0
Rate at which reference rate is fixed		1.50%																																										3.30%
Quarterly principal payment																																																625,000
Variable rate basis																																																			LIBOR			LIBOR
Fixed base rate of variable interest rate																																																	1.50%	1.70%
Note balance		1,081,597,000											14,312,000	14,520,000	0	42,608,000			23,500,000	0	23,500,000	36,000,000	[1]	0	[1]	80,000,000		0	49,317,000	0	117,663,000	0	93,367,000	0	110,000,000	0				16,300,000																								974,062,000	107,535,000
Mortgage notes payable		1,097,493,000	605,889,000																																																						117,700,000	110,000,000	93,400,000	321,000,000		49,300,000	49,300,000
Aggregate annual maturities of mortgage notes payable [Abstract]
2014		11,896,000																																																														0	11,896,000
2015		31,983,000																																																														14,013,000	17,970,000
2016		262,640,000																																																														244,746,000	17,894,000
2017		124,746,000																																																														107,939,000	16,807,000
2018		212,713,000																																																														193,952,000	18,761,000
Thereafter		437,619,000																																																														413,412,000	24,207,000
Total principal maturities		1,081,597,000											14,312,000	14,520,000	0	42,608,000			23,500,000	0	23,500,000	36,000,000	[1]	0	[1]	80,000,000		0	49,317,000	0	117,663,000	0	93,367,000	0	110,000,000	0				16,300,000																								974,062,000	107,535,000
Fair value premium on mortgage debt acquired		15,896,000																																																														0	0
Total mortgage maturities		$ 1,097,493,000										$ 15,700,000				$ 42,977,000																												$ 22,500,000		$ 80,000,000	$ 84,500,000																	$ 974,062,000	$ 107,535,000

[1] Property has entered into an interest rate swap agreement with the Lender associated with these mortgage loans.